Well before, and well after Romeo and Juliet, lovers have lived with parents who disapproved of their match. Even in cultures where parents held—or hold—absolute control over their children’s choice of a spouse, parents and children can clash over love.

For evolutionary scholars, this struggle is especially intriguing. Why, if it causes so much angst, conflict, and, as in Romeo and Juliet’s case, death, do parents (and young lovers) never learn? From a strictly energy efficiency perspective, such drama is far from adaptive — rather, it’s a drain on precious emotional and physical resources. And generally such wasteful behaviors don’t survive generation after generation, as disapproving parents and rebellious lovers have. So why has this conflict persisted so obstinately throughout history?

Turning to a computer model, researchers at the University of Bristol and the University of Groningen have ventured provide an answer. In a study published in the journal Evolution & Human Behavior, they propose that genes may have a lot do with it.

Evolutionary theory suggests that parents and their daughters (and sons, for that matter) should both want a caring and supportive mate. That would work for all of them. And they do both strive for this. But parents, apparently, want it more. The study’s co-author Tim Fawcett, an evolutionary biologist at the University of Bristol, this model of parental and filial behavior is predicated on the fact that parents presumably value all of their children (and therefore the survival of their genes) equally. So parents want to allocate their resources optimally and make sure that each child ends up with equal share. But if one daughter marries the hunky but unreliable handyman and the other comes home with the gawky, devoted investment banker, the former will probably require additional investment of time, money and emotional support to survive, and the others will get less from the parents.

Spending their resources that way may not seem appealing to parents, but, says Fawcett, “it is in their evolutionary interests to do so. The conflict arises because daughters will settle for a partner who provides less support than her parents would ideally like.” In other words, parents feel a need to fill in the gap for the child married to the handyman so that daughter, and her hunk, have the same chance of raising a family and having children who continue the genetic lineage as the daughter married to the wealthy banker.

As for the daughter, she gets the mate she’s most attracted to, she benefits from more help than her siblings receive, and her parents will supply what her husband can’t. So she’s not necessarily pressured to find and marry a mate that meets with her parents’ approval.

There’s another reason this may work for the daughter on an evolutionary basis, says Robert Kurzban, an evolutionary psychologist at the University of Pennsylvania who was not involved in the study. She may be better equipped than her parents at recognizing a guy who’s got good genes and will give her more children — despite his less than stellar supportiveness. In the study, evolutionary success was defined by which daughters had the most offspring who lived to reproductive age. And daughters who chose a mate with fewer resources (and who received more parental support than their siblings did) did indeed have more children. Previous research also showed that parents tended to prioritize social class and family background for a son-in-law while daughters placed greater value on physical attractiveness, sense of humor, and even smell, which some scientists believe helps people identify lovers with compatible genes. All of these, in the end, may help them to populate the next generation.

But will a star-crossed couple be happier? The study makes no such claims. “These models,” says Kurzban, “are trying to give us a sense of human evolutionary history without making any judgment on modern mores. They make no claims that a daughter’s strategy of marrying despite parental disapproval will lead to marital happiness or even to having more children.” What they do suggest, however, is that defying parents when it comes to choosing mates isn’t just a matter of the heart — or of misbehavior — but one of genes and survival. If only the Montagues and Capulets knew.